The present invention relates to a sintered material suitable for the production of structural parts which necessitate wearing resistance and damping capacity.
It has been known that self-lubricating property is imparted to a bearing in case a liquid or semifluid lubricant cannot be used, by producing a sintered material by mixing powdery iron, copper, aluminum, cast iron or an alloy thereof with powdery lead or graphite, compression-molding the mixture and sintering the molding under a reducing atmosphere. If the sintered material produced by above process slides along a shaft, lead or graphite contained in the material is molten by a friction heat to flow on the sliding surface, thereby working as a lubricant.
For example, in Japanese Laying-open of Patent Applications No. 48-13207 (1963) and No. 50-147411 (1975), there are disclosed sintered materials and methods of producing the same which comprise mixing powdery iron or powdery copper with powdery lead or powdery graphite, subjecting the mixture to compression molding and sintering the molding product in a reducing atmosphere. However, the sintered materials produced by those methods have only an insufficient damping capacity due to a form of lead or graphite distributed in the matrix metal such as iron or copper, though they have a high wearing resistance.
Namely, since the conventional methods of producing a sintered material comprise steps of mixing metal powders together, compression-molding the mixture under a pressure of several kilograms per cm.sup.2 and sintering the compression-molded mixture at a high temperature, lead or graphite is aggregated in nearly spherical form on the crystal surface of the matrix metal in the sintering operation. Consequently, the resulting sintered material has only an insufficient damping capacity. For improving the damping capacity, it is desirable that lead or graphite is distributed uniformly in the form of spindles in the matrix metal.